Imaging process

ABSTRACT

VANADYL AND TITANYL PHTHALOCYANINE COMPOUNDS AS ELECTRICALLY PHOTOSENSITIVE PIGMENTS IN PHOTOELECTROPHORETIC IMAGING.

July 23, 1974 R, 1 GRUBER ET AL 3,825,422

IMAGING PROCESS l Filed Oct. 26, 1972 us. c1. 96--1 PE 3,825,422 Patented July 23., l1974 IMAGING PROCESS Robert J. Gruber and Bernard Grushkin, Pittsford, N.

assignors to Xerox Corporation, Stamford, Conn. Filed Oct. 26, 1972, Ser. No. 300,958 Int. Cl. G03c 5/06 8 Claims ABSTRACT F THE DISCLOSURE Vanadyl and titanyl phthalocyanine compounds as `electrically photosensitive pigments in photoelectrophoretic imaging.

BACKGROUND OF THE INVENTION 'Ihe invention relates in general to imaging systems.

-More specifically, the invention concerns the use of vanadyl and titanyl phthalocyanine in photoelectrophoretic imaging systems.

In general, photoelectrophoretic imaging, as used herein, refers to those systems wherein electrically photosensitive particles dispersed in an insulating carrier liquid are exposed to imagewise light and an electrical field resulting in particle migration in image configuration. One such process which is capable of producing one color or more or natural full color images in one step is described in f detail and claimed in U.S. Pats. 3,383,993 to Yeh; 3,384,488 and 'g 3,384,565 to Tulagin and Carreira; 13,384,566 to Clark, all issued May 21, 1968. In such an 1 imaging system, electrically photosensitive particles are dispersed in a relatively non-conductive liquid carrier. The

ticlesare formed on one or both electrodes. In a monob-chromatic system, particles of only one color need be used, but particles of many colors may be used if desired to provide a range of monochrome colors which may be reproduced. In a polychromatic system, images of more than one color may be formed by utilizing particles of more than one color which have spectral response curves which dov not have substantial overlap thereby providing .f lfor kcolor separation. In a preferred embodiment for subtractive full color imaging yellow particles are used responsive mainly to blue light, cyan particles are used which are responsive mainly to red light and magenta parvticles are used which are responsive mainly to green light. Thus, when the suspension is exposed, for example,

-torareas of the original to be copied which are red, the

red'light causes the cyan particles to migrate leaving the yellow and magenta which combined appear red. Further,

where white light impinges the suspension, all particles v migrate leaving a clear area which when transferred to white paper appears white. Similarly, where no light irnpinges the suspension, all particles remain which form a dark brown or black area. i Y

The critical component of such an imaging system is .i the. velectrically photosensitive particles. They must have intense and pure colors to form pleasing highly saturated vpkimages. `For monochrome images, the particles should :have highphotosensitivity, and it is often desirable that they be panchromatic so as not to ybe blind to one area of the spectrum. The requirements for subtractive polychrome particles are more severe in that not only wmustthey have intense and pure colors but their spectral A response curves must be well-defined and not overlap the spectral response curves for particles of other colors.

Further, the photoresponse of a given particle must be to approximately the same intensity of exposure as the other particles to provide color balanced images. For example, in a subtractive system, if the particle is too photoresponsive or has too broad a spectral response, the final image will be deficient in that color. Conversely, where the particle is too slow, the image formed will have a high background and will have poor color balance. For additive systems, the results, of course, would be reversed.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide photoelectrophoretic imaging systems which overcome the above noted problems.

It is another object of this invention to provide a photoelectrophoretic imaging suspension having improved photoelectrophoretic imaging characteristics.

It is another object of this invention to provide new electrically photosensitive particles for use in photoelectrophoretic imaging systems.

The foregoing objects and others are accomplished in accordance with this invention by providing photoelectrophoretio imaging processes utilizing vanadyl phthalocyanine or titanyl phthalocyanine or mixtures of vanadyl phthalocyanine and titanyl phthalocyanine. The titanyl and vanadyl phthalocyanines may be substituted or unsubstituted. Phthalocyanine, which is also known as tetrabenzotatraazaporphin and tetrabenzoporphyrazine, may be considered as the condensation product of four isoindole groups. Phthalocyanines may be metal-free or metal-containing and are very well-known. One book describing phthalocyanine compounds in detail is Moser et al., Phthalacyanne Compounds ACS Monograph 157, Reinhold Publishing Co. (1963).

In a preferred photoelectrophoretic imaging process, finely divided particles of electrically photosensitive particles are dispersed in an insulating carrier liquid and coated onto a transparent conductive electrode called the injecting electrode. A second electrode having an insulating outer surface and called a blocking electrode is caused to contact the free surface of the suspension. An electrical field of relatively high potential is applied across the suspension between the electrodes while the suspension is exposed through the injecting electrode to a pattern of electromagnetic radiation of wavelengths to which at least some of the particles are responsive. On completion of these steps, normally a positive image is found adhering to the injecting electrode and a negative vimage is formed on the blocking electrode. Apparently,

the particles which are within interaction range of the conductive injecting electrode when struck by light tc which they are sensitive exchange charge with the injecting electrode and are repelled by it migrating to the :blocking electrode leaving behind a positive image. The particles which migrate to the blocking electrode are less able to exchange charge with the insulating surface and adhere to it forming a negative image. v The process of photoelectrophoretic imaging and the materials used are set out in detail in the abovev mentioned patents 3,383,993; 3,384,488; 3,384,565 and 3,384,566, the disclosures of which are incorporated herein by reference. v

The use of phthalocyanine compounds 'generally'in photoelectrophoretic imaging, is disclosed and claimed in UJS. Pat. 3,615,558 to L. Carreira and V. Tulagin, issued Oct. 26, 1971. =In this patent substituted and unsubstituted, metal-containing and metal-free phthalocyanines are disclosed and claimed. There is, howeverVno disclosure as to the specific useof vanadyl or titanyl phthalocyanines in photoelectrophoreticI imaging and the unexpected results obtainable therewith.

invention may comprise any suitable insulating material. Typical insulating materials include liquids or materials y, which may beconverted to a liquid at thei time of particle migration. Typical insulating liquids include: decane, .dodecane, tetradecane, kerosene, molten paraffin, molten beeswax or other moltenthermoplastic material,V mineral 4oil, silicone oils such as dimethyl polysiloxane, fluorinated hydrocarbons and mixtures thereof. Mineral oil and kerov serrerarepreferred because of their excellent insulating qualities.A l

' Alternatively,vthe particles may be pre-coated on one of the electrodes in a solid binder such as Piccotex polystyrene resin available from Pennsylvania Industrial Chemical Co. or eicosane wax for ease of handling and storage. The binder is melted or dissolved by a dielectric solvent such as those listed above prior to imaging so that the particles are free to migrate. Other typical solvent-soluble dielectric binder materials include hydrogenated rosin esters such as Stabelite Esters 5 and 10 available from Hercules Powder Co., phenolformaldehyde resins such as Amberol ST-l37-X available from Rohm and Haas, and Piccotex 75 and 100 and Piccopale 70 SF available from Pennsylvania Industrial Chemical Co.

vIt is desirable to use particles of a relatively small size because small particles provide a more stable suspension and provide images of higher resolution than would be possible with larger particles. Particles of less than one or two microns in average cross section are preferred although particles up to about 5 to 10 microns may be used.

The concentration of particles dispersed in the liquid depends on a number of variables including operating conditions, the density of the nal image desired, the use to which the image is to be put, the solubility of added dispersants and other factors generally known to those p skilled in the art of ink or plastic coating formulation.

The transparent conductive substrate may comprise any suitable material. Typical transparent conductive materials include conductively coated glass, such as aluminum or tin oxide coated glass or transparent plastic materials pared by conventional methods. Preferred methods for f preparing these compounds for photoelectrophoretic imaging are shown in the following Examples.

EXAMPLE I Vanadyl phthalocyanine is prepared as follows: a mixtures of 247 grams of phthalic anhydride, 247 grams of urea, 3 liters of chloronaphthalene and 100y grams of vanadium trichloride is refluxed at 255 C. for 45 minutes, cooled to 25 C. and filtered. The solid is washed with 300 ml. of ethanol, then slurried in 100 ml. of ethanol for 2 .hours and iilteredfThe Wet pigment is then thoroughly Washed at 70.1.C.using first, 2 liters of 10% sodium hydroxide, the-n 2 liters `of 20%.HC1 and then 2 liters of n,deionized,.waten The wet cakeis air driedthen vacuum Av clried.at`,65"` l A, y 15H-grams of the thus prepared crude Vanadyl phthaloeyanine is .dissolved 'in 40, ml. of concentrated sulfuric .acid

then filtered through a coarse fritted funneland sprayed intooneliterof-,water and againEfiltered using. a medium porosity funnel. ,.The-materialgis extensively wash,ed-.in :Mater 'nluding a wash with 750 ml. of water containingv ,1.8 mlof concentratedammonium hydroxide.l The Vanadyl phthalocyanine is '-air-Qdriedfand thenl .vacuum driedfat 'Toa 1 EXAMPLE 11 -liter ask, fitted withy a thermometer and set up for distillation, is added 12.3 grams l(0.08 mole) of titani- 'I`he carrier liquid for the imagingsuspension of this um tric-blonde, uZO--grams -(0.16-mole).ofo-phthalonitrile and 375 ml. of alpha-chloronaphthalene. The flask is heated under a blanket of nitrogen while being stirred with a magnetic stirrer. When the temperature is at approximately 170, an orange-red liquid begins to distill. The temperature is raised Isteadily to 255 C. (reflux) and is maintained at 255 C.. for-one hour. Thetprodi'ict isthen cooled to room temperature; Afteriltering; the isolid is washed withY dry benzene and 375 ml' portions of anhydrous ether. The solid is then dried'undervacuumtq; giye 20.7 grams of TiClZPc. A mixture of 1.8 grams of TiClPc, 1 liter of 95% ethanol, and 20 ml. of pyridine is reliuxed with stirring for 3.5 hours.l Aftercooling-tdroom temperature, the reaction mixture isiiltered andthe sollidfwashed with 200 ml. of ehtanol. In this manner, 4there y,iy btaiued 14.2 grams of a blue solid whose infrared s pectruirfA is similar to that reported for (TiOPc)X. j

The crude titanyl phthalocyanine thus prepared is acid pasted by dissolving 6.8. grams offlfiQPc -in 1.00 ml. of concentrated sulfuric acid then, after one hour, the sulfuric acid solution is carefullyfpouredfonto -llliterof crushed ice, ltered, and washed with l00fml. 'of deionizedwter until it is no longer acidic. 'The resulting 'wetlakeis slurried for one hour two times in the following solutions at 70 C.; water, dilute ammonium 'hydroxide',l'a'fnd finally again, water. The pigment1 'is'thenair dried'iove'rn'i'ght followed by vacuum drying 'at 65 andQO-inm.v for.l 24 hours. 4.9 grams of acid pastedTiOPc isobtained. y'

`In a 500 ml.`3 necked flask; fitted-:with azcond'enser stirrer and heating mantel, is placed=10"g. (0.064Hmo`l) vanadylphthalocyanine.

l "BR miD DESCRIP', IONF. No. i'

of vanadium trichloride, 25 g.' '(0.172 mol)fof.-'l,3-di iminoisoindole and 250 ml. -of chloronaphthalenei'@The mixture is slowly heatedlto reux overalhourperiod and then held at refluxl'for :an adlitionfal .-5fhurs'.'-=After iiltering at 65 C., the solid'is'washed .wi-thHBOOVmlwof acetone, then slurried in 500 m1; of-ethnbllovernight followed by two slurrings'in v10% sodiumhydroxidef-for 2 hours at 70 C. and twicein 20%- khydrochloric-acid also for 2 hours at 70 C. Thesolid is furtherwash'ed with deionized water 'and driedv at 65 und'e'r"vaei1urn"to give 18.2 g. (48.8%) fof Vanadyl'phthalocyanineffffif This reaction can be carried out in ethylene f'glycol, quinoline or other suitable high boiling solventl.'-"There -action also can be carried out using vanadiumtetrachloride or vanadium oxychloride. f Y

EXAMPLE. 0.5-5 mole of vanadium tetrachloride'and10t5nlole'ffof metal free phthalocyanine in 3 liters-'of-trichlorobenzehe is heated to reflux for 5'hoursxThe mixture isf-then cooled and filtered. The solid is washedawith.acetonathanolfand then a 10% sodium hydroxide, 10%fhydrochlorictacid, and finally water. After'drying the. crude productrisdissolved in concentrated H2SO4f(1 gramin 50.finl.5acid) and poured into water. :yield olvanadylhthalocyanine is recovered. f f

, p EXAMRLII/v. The experiment of Example IVis ,repeatedexceptfxiisodium phthalocyanineJisused'providingia 907 yield-tof 1 EXAMPLE VI yield ofvanadyl phthalocyanine'is1obtained/ yThe advantages of this` improved Vgn,ing will vbecomeAapparentf'upon consideratibno thele.

tailed disclosure of this invention, paticularlywlien conp The sige'sand shapesffmfthe drawingsfshould no tbe loilsidftred as ,actlial sizesjorfeye'n proj'no'rtionalk to actual sizes because4v many ofthe elements` havebeen purposely distorted in size to moreufully .and clearly describe the invention. v

Referring now lto the Figure, there' is seen a transparent' a electrode generally designatedl, which in this exemplary instance, is madeupyof a layer of optically transparent glass 2 overcoated with a thin optically transparent layer 3 of tinoxide, commercially available under the name NESA glass. This electrode will be referred to as the injecting electrode. Coated on the surface of injecting electorde 1 is a thin layer 4 offinely'dividedphotosensitive particles dispersed in an insulating .liquid carrier. The term electrically photosensitive', for the purposes of thisv application, refers to the properties of a particle which.l when brought into interaction range of the injecting electrode, will migrate away from it under the inliuence of an applied electric iield when it is exposed to radiation to which it is responsive. Liquid suspension 4 may also contain a sensitizer and/or a binder for the particles which is at least partially soluble in the suspending or carrier liquid. Adjacent to the liquid suspension 4 is a second electrode 5, blocking electrode which is connected to one side of potential source 6 through switch 7. The opposite terminal of potential source 6 is connected -to the injecting electrode and ground so that when switch 7 is closed, an electrical field is applied across the liquid suspension 4 between electrodes 1 and 5. An image projector made up of light source 8, a transparency 9 and a lens 10 is provided to expose the suspension 4 to a light image of the original transparency 9 to be reproduced. Alternatively, the image may be light reected off of an opaque picture or document. Electrode 5 is in the form of a roller having a conductive central core 11 connected to potential source 6. The core is covered with a layer of an insulating material 12. The suspension is exposed to the image to be reproduced while a potential is applied across the blocking and injecting electrodes by closing switch 7 and causing roller 5 to roll across the free surface of suspension 4 during image'wise exposure. On completion of roller traverse, a positive image is found on electrode 1 and a negative image is found on surface 5. During roller traverse, the roller is pressed into virtual contact with the injecting electrode surfaces. Gaps of up to about one mil. are used. Voltages of from about 300 to 5,000 volts are used in the apparatus as shown in the Figure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following Examples further specically illustrate the improved photoelectrophoretic imaging system using the compositions of this invention. Parts and percentages are by weight unless otherwise indicated. 'Examples VII and VIII are carried out in an apparatus of `the general type illustrated in the figure with the imaging suspension coated on the conductive surface of a NESA glass plate through which exposure is made. The NESA glass surface is connected to a source of high D.C. potential and ground. The other terminal of the source of high potential is connected to a steel roller about one inch in diameter having a 1%" layer of polyurethane having a resistivity of about 5 X109 ohm. cm. forming a 21/2 inch rol-ler. A paper sheet is placed over the plastic to receive migrating particles. The particles are dispersed in the liquid carrier and ball milled until the average particle size is less than about one micron and a stable suspension is formed. The roller is moved across the plate surfaceat a. rate of about 3 inches/secondl and the image )is projected using t a conventional tungsten lamp. The :transparency may be black and white or color as indicated.

' glass plate to a thickness of about 2 mils. Roller potential is about 2500 volts, the roller being biased negative with respect to the injecting electrode. Exposure is l'made 'through a 0.30 neutral density step wedge lilter tolmeasure the 'sensitivity of the suspension to white light and then Wratten 29, 61 and 41b filters are individually superimposed over the light source in separate tests to measure the sensiti-vity of the suspension to red, green and blue light, respectively. The reciprocal of spectr-al sensitivity is given in microwatts/cm.2, being the result of a curve of optical density plotted against the intensity of exposure in m-icrowatts/cm-2, the time of exposure being held constant. This is the method used to determine the photographic speed of the photosensitive material. Sensitivity to blue light was found -to be 200mm/cm?, to green light mw./cm.2, to red light 18 mw./cm.2 and 18 mw./cm.2 to white light.

EXAMPLE VIII The experiment of Example VII is repeated except that the titanyl phthalocyanine prepared as in Example VII is used in place of the vanadyl phthalocyanine. Sensitivities were determined to be 200 mw./cm.2 to blue light, 100 rnw./cm.2 to green light, 20 mw./cm.2 to red light and 2O mw./cm.2 to white light.

It has been found through extensive testing that the sensitivity to red light is greater for the vanadyl and titanyl phthalocyanines than for the metal free or copper phthalocyanines shown in the prior art. Further, the absorption of the green and blue wavelengths for the vanadyl and titanyl phthalocyanines is less than that of metal free or copper phthalocyanine. The vanadyl and titanyl phthalocyanines are superior cyan colorants for use in polychromatic imaging. The vanadyl and titanyl phthalocyanines provide a larger range of green reproduction than do prior art pigments. Those characteristics are extremely important for a full color subtractive imaging process where accurate color separation and reproduction are required.

The improvements obtained were further confirmed in full color subtractive imaging using their vanadyl phthalocyanine or titanyl phthalocyanine in combination with a yellow pigment and a magenta pigment as shown in Examples XI through XVI of U.S. Pat. 3,615,558, the disclosure of which is incorporated herein by reference.

Although specific components and proportions have been described in the above Examples, other suitable materials, as listed above, may be used with similar results. In addition, other materials may be added to the pigment compositions to synergize, enhance or otherwise modify their properties. The pigment compositions where desired, for example, may be coated with a plastic.

Other modifications and ramiiications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

IWhat is claimed is:

1. A method of photoelectrophoretic imaging which comprises the steps of:

(a) forming a layer of an imaging suspension, said imaging suspension comprising inely divided el`ectrically photosensitive particles dispersed in an insulating carrier liquid; A

(b) subjecting said laer of a suspension to an electric eld; and,

(c) exposing said suspension to a pattern of activating electromagnetic radiation to which at least a e meth vd of" lairn particles of a different color. y

5. The method of claim 1 wherein said p articles comprise Vanadyl phthalocyanine responsive mainly to red light, a yellow particle responsive mainly to blue light and a magenta particle responsive mainly to green light.

6,. The method of claim -1 wherein said particles comprise titanyl phthalocyanine responsive mainly to red light, a yellow particle responsive mainly to blue light and a magenta particle responsive mainly to green light.

l L lwwheire'in' sajidl suspension@ omprisesfpartils oufrrnore than onecoloir, said particles of one'color, hvinga photosensitive lresponse whichdoes .not substantially overlap the photosensitive response .of

3,664,941 5*/-1972-1; rzoNALD H.. SMITHy I. L. GooDROWjA's 

